Nitrogen-fertilized grasslands may produce six times more pollen than their unfertilized counterparts, according to a recent study published in The Lancet Planetary Health. The study also suggests that pollen from fertilized grasslands is more likely to trigger hay fever than pollen from unfertilized grasslands.
The rise in pollen allergies globally over recent decades has been attributed to various factors, including atmospheric nitrogen pollutants affecting pollen and leading to an increased release of allergens. However, little research has been conducted on the impact of nitrogen fertilizers, a significant source of environmental pollution, on pollen.
In this study, pollen samples from 25 nitrogen-fertilized and 25 non-fertilized grasslands in Belgium were compared. The results showed that the average pollen count in the fertilized grasslands was 3.6 mg/m2, which is 6.2 times higher than the unfertilized grasslands with 0.6 mg/m2 of pollen.
Furthermore, the study assessed the allergenicity of the pollen by exposing the blood of 20 individuals to pollen from both types of grassland. The participants’ immune cells (basophils) were found to be five times more sensitive, on average, to the pollen from the fertilized grasslands compared to the unfertilized grasslands.
The authors suggest that further research should involve exposing participants to pollen from both types of grasslands and studying their immune response to confirm the allergy-triggering effects of nitrogen-fertilized pollen.
This study is the first to establish a clear relationship between nitrogen fertilizer use, pollen count, and its ability to trigger allergies. The findings underscore the urgent need for strategies to address not only the impact of nitrogen fertilizer on biodiversity and the environment but also the human health implications of nitrogen pollution.
For more information, the study titled “The impact of ecosystem nitrogen enrichment on pollen allergy: a cross-sectional paired comparison study” by Robin Daelemans et al. can be found in The Lancet Planetary Health (2025) with DOI: 10.1016/S2542-5196(25)00060-9.
In conclusion, the study highlights the potential supercharging effect of nitrogen fertilizer on allergy-causing pollen and emphasizes the importance of addressing nitrogen pollution for both environmental and human health reasons.
